Comments on: Wooster’s Fossil of the Week: A crinoid-rich Lower Carboniferous siderite concretion (part II — the inside story)http://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/
A World to ExploreThu, 14 Dec 2017 00:27:55 +0000hourly1https://wordpress.org/?v=4.9.1By: Mark Wilsonhttp://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/comment-page-1/#comment-54144
Sat, 18 Jan 2014 18:33:10 +0000http://woostergeologists.scotblogs.wooster.edu/?p=9316#comment-54144That’s a good idea, Bill, the I.S. possibility. I wouldn’t be the advisor, but maybe Meagen Pollock would be interested. We would also have to find additional specimens with provenance. I’m glad these beautiful fossils provoked such an interesting analysis!
]]>By: Bill Reinthalhttp://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/comment-page-1/#comment-54090
Sat, 18 Jan 2014 13:37:21 +0000http://woostergeologists.scotblogs.wooster.edu/?p=9316#comment-54090BTW, there’s an I.S., just in that one specimen, if you have, or have access to, the equipment to analyze, in detail, the chemistry of the minerals as you traverse the surface, particularly at the interfaces between the mineralogic transitions.
]]>By: Bill Reinthalhttp://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/comment-page-1/#comment-54089
Sat, 18 Jan 2014 13:32:53 +0000http://woostergeologists.scotblogs.wooster.edu/?p=9316#comment-54089Well, the marcasite in the crinoid stems is spectacular, and a lot of near surface (well, anywhere you can get water to flow through rock, so “near surface” is a rather relative term), water-mediated reactions are controlled by oxidation-reduction equilibria. Just like in the classic “roll-front” uranium deposits of the desert SW, or the banded iron formations, we see the oxidation state of the fluid controlling deposition of, in those cases, valuable concentrations of metals (or metal oxides), and it is very common to see metals either oxidized (as carbonates or oxides or sulfates, etc.) change over into sulfides (dominantly) as the fluids which mediate the reaction have their oxidation state controlled by the rocks (and, particularly, the rocks’ composition) through which they flow. Sorry for that rather long sentence.
]]>By: Mark Wilsonhttp://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/comment-page-1/#comment-54050
Sat, 18 Jan 2014 01:58:45 +0000http://woostergeologists.scotblogs.wooster.edu/?p=9316#comment-54050That makes sense to me as a possibility, Bill. There must be a chain of mineral reactions and transformations here, all beyond my skills to decipher! I am impressed with your mineral chemistry.
]]>By: Bill Reinthalhttp://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/comment-page-1/#comment-53973
Fri, 17 Jan 2014 10:08:02 +0000http://woostergeologists.scotblogs.wooster.edu/?p=9316#comment-53973That is a great set of photos! It’s possible that the marcasite represents the reduced form of other iron oxides/carbonates (hematite and sideritic carbonate) in the surrounding concretion material. If there were enough residual carbon remaining in the body/stem of the crinoid, and since we know there was plenty of sulfur from some source, the carbon may have acted to reduce the oxidation state within the body cavity to allow formation of iron sulfide as opposed to iron carbonate/oxide. It would be interesting to see if a chemical analysis of the surrounding concretion material showed sulfate in the matrix. So, you may be seeing a simple oxidation-reduction “equilibrium” reaction at work due to the presence of the gradient between and oxidizing and reducing environment. It’s analogous to the reaction we see in, and around, Ohio coal beds, where ancient seawater sulfate has been reduced to iron sulfides because of the reducing conditions in the coal.
]]>By: Mark Wilsonhttp://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/comment-page-1/#comment-53581
Tue, 14 Jan 2014 20:15:37 +0000http://woostergeologists.scotblogs.wooster.edu/?p=9316#comment-53581At least it fizzes!
]]>By: old limeyhttp://woostergeologists.scotblogs.wooster.edu/2014/01/12/woosters-fossil-of-the-week-a-crinoid-rich-lower-carboniferous-siderite-concretion-part-ii-the-inside-story/comment-page-1/#comment-53531
Tue, 14 Jan 2014 14:27:17 +0000http://woostergeologists.scotblogs.wooster.edu/?p=9316#comment-53531…just wonder whether the calcite is indeed calcite. It has a slightly greasy lustre. You get various things in some Jurassic concretions that look a bit like calcite but turn out to be Barium or Strontium compounds.